1. Field of the Invention
The present invention relates to a corona wire cleaning device for a corona unit used, for example, as a charge unit, a transfer/separation unit, or the like, in an electrophotographic copying machine.
2. Description of the Prior Art
In an electrophotographic copying machine, a corona unit is used as a charge unit for uniformly charging the photoconductor. Usually, the corona unit includes a corona wire formed of tungsten, platinum, etc., stretched in a box-like shield case. In such a corona unit, when corona discharge is caused by the application of a high voltage, gas of silicon compounds containing silane or the like that is contained in the air surrounding the corona wire forms into a silicon oxide compound which adheres to the surface of the corona wire.
Adherence of the silicon oxide compound substantially impairs the discharging performance of the corona wire. Furthermore, for the corona unit used as a charge unit in an electrophotographic copying machine, adherence of paper dust and toner to the corona wire is also a problem since it reduces the discharging performance of the corona wire. If the discharging performance of the corona wire of the corona unit used as a charge unit is reduced, the photoconductor may not be charged uniformly, resulting in an uneven surface potential of the photoconductor and therefore, hampering formation of a clear image.
As a means to solve this problem, Japanese Laid-Open Patent Publication No. 62-86375, for example, discloses an automatic cleaning device for a corona unit which is used as a charge unit. In such an automatic cleaning device, a cleaning tool which rubs the corona wire, is coupled to a driving motor via a driving wire, the forward and reverse rotation of the driving motor driving the driving wire in the forward and backward direction to move the cleaning tool along the corona wire. While the driving wire is moved backward and forward, the cleaning tool rubs the corona wire to clean it. When the cleaning tool reaches either end of the corona wire, a sensor disposed in close proximity to the end is activated to stop the rotation of the driving motor.
The cleaning tool of this automatic cleaning device for a corona unit is in frictional contact with the corona wire both ways of the cleaning trip. Therefore, there is the possibility that, for example, the foreign material such as dust removed by the cleaning tool on the forward trip and stuck to the side thereof opposite from that facing the traveling direction will once again adhere to the cleaned corona wire during the backward trip of the cleaning tool.
The above automatic cleaning device for a corona unit is provided with a sensor to detect the cleaning tool reaching the prescribed position, and is so constructed that when the sensor has detected the cleaning tool reaching the prescribed position, the motor stops rotating. Since the cleaning tool is thus prevented from moving further when it has reached the prescribed position at the end of the corona wire, there is no possibility of the motor locking due to the application of excessive load. Furthermore, because of high tension applied to the driving wire, there is no possibility of the driving wire breaking. However, since the provision of a sensor is required in order to detect the cleaning tool reaching the prescribed position, there is a problem that the construction is not economical. Furthermore, there is a problem that the installation of the sensor to the prescribed position is troublesome.
In an electrophotographic copying machine, a corona unit is also used as a transfer/separation unit. The corona unit used as a transfer/separation unit usually comprises two wires stretched in one shield case, a corona wire for transfer and a corona wire for separation. If the above-mentioned automatic cleaning device is to be used for such a corona unit, it will be necessary to provide two driving motors, one each for driving the cleaning tool for cleaning one corona wire, and hence uneconomical in construction.